The engine controlling system of a motorcycle is exposed. Therefore, a motorcycle is provided with a handle locking device or the like to prevent theft. No other particular consideration is made on the operating system.
That is to say, conventionally no consideration other than a main switch including an ignition circuit is made on the operating system of the engine. Therefore, while the motorcycle is parked, the throttle grip of the handle can be freely rotated and operated, and is often purposely mischievously rotated and operated by strangers.
Such rotating operation of the throttle grip during the parking or the like causes the following problems.
When the throttle grip is rotated and operated while the engine is not being operated, the fuel will be led into the suction passage to the engine, particularly by a mechanical accelerating pump or the like so that a too rich mixture will be fed at the time of starting the engine. Not only will it be difficult to start the engine, but also the battery will likely be exhausted by the repeated starting operation of the starting self-starter.
Thus, the rotation operation of the throttle grip when the engine is not running will have an undesirable influence on the starting of the engine or the like.